What is ViewPoint doing that Lightroom isn't?
If you're using Lightroom 5 it's probably doing very little, since they added perspective correction software - though I have no idea how good it is.
I've been using Viewpoint for a long time for my architectural work, so I never made the jump to LR5 (still using LR4). The fact it 'bakes it in', as explained above, never really bothered me because my workflow always exported to Photoshop anyway. I just did my adjustments in LR, Edit in Viewpoint, then export to Photoshop.
That said, there have been times that I had to start over because I wanted to adjust something after Viewpoint. I'm curious to see how the Lightroom perspective correction tool matches up with Viewpoint (which I think to be rather good). But the thought of non-destructive perspective correction and not having to enter a new module sounds enticing. Looking forward to Lightroom 6.